The pressure, temperature and chemical conditions in many oil and gas wells are such that considerable difficulty has been experienced in prior packoff and seal ring structures for sealing around tubing, casing or a mandrel in oil and gas wells. Resilient seals have been subject to permeation problems, extrusion and breakdown when subjected to the elevated temperatures and high pressures encountered in such wells. Further, many of such wells contain fluids and gases which may chemically attack the resilient material of such seals.
Use of metal-to-metal seals in such applications has required selective sizing with respect to the outside diameter of the inner sealing surface.
Most current seals are resilient seal rings which require an anti-extrusion device but anti-extrusion devices, such as shown in U.S. Pat. No. 4,219,204 are not applicable when there is a large range of gap widths to be bridged. Such range results from allowed tolerances in the manufacture of oil field tubular goods. Further, such seals cannot be reenergized without internal manipulation.
U.S. Pat. No. 3,797,864 discloses a seal for a casing hanger including a resilient ring with metallic end rings and having marginal lips which are moved into sealing engagement by axial compression exerted on the resilient ring. However, such construction, while possibly providing sufficient backup to prevent extrusion, does not establish a true metal-to-metal seal.
A prior valve seat seal is disclosed in U.S. Pat. No. 2,457,493 which includes a rubber seat ring having metal confining rings at the upper and lower outer corners of the rubber seat ring. However, it is not clear how this valve construction could suggest a solution to the present problem.